1. Field of the Invention
The present invention relates to an accumulator, more particularly, to an accumulator that is adapted, in a non-normal operation in which a pressure and a temperature in an air chamber increase more excessively than in a normal operation, to release the pressure in the air chamber through a gap portion formed between a self-sealing member and a seal face facing the self-sealing member.
2. Description of the Related Art
A fluid-pressure circuit such as a braking circuit used in an automobile employs an accumulator that temporarily accumulates pressurized fluid. Formed in the accumulator are an air chamber adapted to allow high-pressure gas to be filled therein, and a fluid chamber adapted to allow pressure fluid (hydraulic oil) from the fluid-pressure circuit to be introduced thereinto. The air chamber and the fluid chamber are arranged to face each other across an elastic bellows, and the bellows is allowed to expand and contract, thereby balancing the pressure in the air chamber with the pressure in the fluid chamber to suppress pulsation in the fluid-pressure circuit to regulate its fluid pressure to an appropriate value.
Such an accumulator has heretofore had a possibility that an internal pressure of the air chamber of the accumulator excessively increases, for example, when the automobile encounters a fire or the like to be placed in a high-temperature environment for a long time. To cope with this, the accumulator is provided with a relief means for emergency evacuation that releases the internal pressure of the air chamber when it encounters such an abnormal state (for example, Patent Document 1: Japanese Patent Application Publication No. 2003-172301, and Patent Document 2: Japanese Patent Application Publication No. 2006-010005).
Patent Document 1 describes an accumulator (see paragraph [0017] and FIG. 1) in which, as a relief means that releases the internal pressure of the air chamber, the fragile portion 11 is formed with a reduced thickness at a portion of the side wall of the stay 4 arranged in the fluid chamber 8. This accumulator is adapted, when the internal pressure of the air chamber excessively increases, to allow the bellows to be compressed with the excessively increased internal pressure of the air chamber to increase the internal pressure of the fluid chamber 8, thereby breaking the fragile portion 11.
Moreover, the accumulator is adapted, with the fragile portion 11 being broken, to discharge high-pressure pressure fluid from the fluid chamber 8 to decrease the pressure in the fluid chamber 8, thereby damaging the bellows purposefully with the excessively increased internal pressure of the air chamber to release the internal pressure of the air chamber.
Patent Document 2 describes an accumulator (see paragraph [0027], FIG. 3 and FIG. 4) in which, as a relief means that releases the internal pressure of the air chamber, the groove 62 is formed on the surface (first portion 61) of the base material 56 of the self-sealing member 55 which is allowed to abut onto the dividing wall 35 forming the seal face. This accumulator is adapted to discharge the fluid Q in the fluid chamber 50 through the groove 62 to the outside of the shell 11 to decrease the pressure in the fluid chamber 50, thereby damaging the bellows purposefully with the pressure difference between the air chamber and the fluid chamber to release the pressure in the air chamber 51.
However, the accumulator described in Patent Document 1 has posed problems in that machining of the fragile portion 11 is complicated and thus accuracy control for the machining is required to increase a machining man-hour and to decrease production efficiency.
Moreover, the accumulator described in Patent Document 2 has posed problems in that, since the groove 62 is formed on the surface (first portion 61) of the base material 56 of the self-sealing member 55, every time the resilient member 57 arranged to cover the surface of the base material 56 abuts onto the seal face 35a of the dividing wall 35, the resilient member 57 is gradually damaged to affect sealing performance and/or duration of life.